1. Field of the Invention
The present invention relates to large-capacity magnetic recording media, and in particular to a magnetic recording medium having superior magnetic recording properties and transport characteristics.
2. Description of Related Art
Magnetic tape, which is one type of magnetic recording media, has a variety of applications such as audiotape, videotape and computer tape. Especially, in the field of computer data backup tape, tapes having a recording capacity of several hundred gigabytes per reel have been commercially available as the capacity of hard disks to be backed up has increased. In the future, it will be essential to increase the capacity of such data backup tape in order to support further increases in the capacity of hard disks.
With regard to a magnetic tape for use as the data backup tape mentioned above, the recording wavelength has been shortened with the further increase in the recording capacity, and in order to reduce thickness loss during recording/reproduction, an effort has been made to reduce the thickness of the magnetic layer of the tape. To achieve the reduction in the thickness of the magnetic layer, a magnetic recording medium having a multilayered structure has been adopted. In the multilayered magnetic recording medium, a non-magnetic layer is provided on a non-magnetic substrate and a magnetic layer is further provided on the non-magnetic layer.
For such a multilayered magnetic recording medium, studies have been conducted to reduce noise by reducing variations in the interface between the magnetic layer and the non-magnetic layer (see JP 2001-256633 A, for example). Further, there has been proposed a magnetic recording medium in which the average thickness of the magnetic layer and σd as the standard deviation of the magnetic substance distribution in the thickness direction of the magnetic layer, in particular in the interface between the magnetic layer and the non-magnetic layer are specified (see JP 2007-294083 A, for example).
JP 2001-256633 A discloses a multilayered magnetic recording medium in which d as the average thickness of the magnetic layer is 0.01 to 0.3 μm, and the ratio of σ as the standard deviation of the thickness of the magnetic layer to d as the average thickness of the magnetic layer (σ/d) is ≦0.5.
Further, JP 2007-294083 A discloses a magnetic recording medium in which 6 as the average thickness of the magnetic layer is 10 to 100 nm, and σd as the standard deviation is 5 to 50 nm in terms of coating layer in the magnetic recording medium, where σd is obtained by measuring by TOF-SIMS a depth profile of an element present only in the magnetic layer among elements constituting the ferromagnetic powder and subjecting a differential curve of the depth profile to a normal distribution curve fitting.
In JP 2001-256633 A, a picture of the cross section of the magnetic layer is taken under a transmission electron microscope (TEM), the surface of the magnetic layer and the interface between the magnetic layer and the non-magnetic layer are each traced to determine the thickness of the magnetic layer at each point, and the standard deviation is determined relative to the variations in the thickness. On the other hand, in JP 2007-294083 A, attention is focused upon the element present only in the magnetic layer. The depth profile of the element in the interface between the magnetic layer and the non-magnetic layer is measured, and the standard deviation relative to the variations in the interface is determined from the depth profile curve. For a standardization purpose, when σd as the standard deviation of the variations in the interface is divided by δ as the average thickness of the magnetic layer in JP 2007-294083 A, σd/δ is ≦0.5. This indicates that JP 2007-294083 A has the same technical principles as those of JP 2001-256633 A.
By such techniques, improved magnetic conversion characteristics can be expected. However, such techniques may be not sufficient for obtaining a magnetic recording medium having not only improved magnetic conversion characteristics but also superior transport characteristics and durability.
With the foregoing in mind, it is an object of the present invention to provide a magnetic recording medium having not only superior magnetic conversion characteristics but also superior transport characteristics.